The invention relates to a method for detecting a short in a resolver excitation line to ground or to the operating voltage, and it also comprises a circuit for realizing this method.
Resolvers are used to ascertain the angular position of a rotating object, e.g. the driveshaft of a motor. There are various types of resolver in the prior art. Fundamentally, at least one coil is used in this case to produce a changing magnetic field, and at least one further coil is used to detect this field, the strength of the coupling between the coils varying as a function of the position or angular position to be measured. In the case of the “variable reluctance resolver” (VR resolver), for example, only one field coil is used, and there are two measurement coils that produce position-dependent signals. The German patent application DE 10 2011 078 583 A1 discloses evaluation of resolver sensor signals in a vehicle, for example. To this end, a resolver picks up a rotary movement of a rotor, and a processor element processes the sinusoidal and cosinusoidal output signals of the resolver.
The invention is based on such a resolver, the excitation signal being sinusoidal and typically having a frequency of 10 kHz. The two measurement coils are normally positioned orthogonally in relation to one another and are referred to as the sine and cosine coils. The two measurement signals can be used to explicitly determine the angle of the measurement object.
The excitation signal for the field coil can be provided by two push-pull output stages, for example, one for each of the two connections of the field coil. The output signals of the two output stages then have a phase shift of 180° in relation to one another, and the excitation signal effective for the field coil is the difference voltage between the outputs of the two output stages.
There is, however, also the option of the field coil being operated by only one output stage. The second connection of the field coil is then at a fixed potential, e.g. ground potential, either directly or via a capacitor.
On the receiver coils, there appears an AC voltage signal at the same frequency as the excitation signal, the amplitude of which is modulated in accordance with the rotor position, however, the signal on the cosine coil having a 90° phase shift relative to the signal on the sine coil.
Resolvers are frequency used to regulate permanently excited synchronous machines (PSM) and electrically excited synchronous machines (ESM), which are used e.g. as a drive for hybrid and electric vehicles. Such regulation requires knowledge of the present rotor angular position. Regulation of asynchronous machines (ASM) requires knowledge of the present frequency of the drive.
Their robustness means that resolvers are preferably used for these purposes in motor vehicles, even if there are alternative sensors, e.g. digital angle sensors or sensors based on the eddy current effect.
Sensors in the automotive field need to be diagnosed to meet requirements of functional safety and legislation. In the case of resolvers such as the present application relates to, a possible fault to be diagnosed is a short in a resolver excitation line to ground or to the operating voltage. In this case, a short is subsequently understood to mean only an unwanted electrical connection from one of the connections of the resolver excitation line to ground or to the operating voltage, the diagnosis also being intended to establish which of these potentials has the unwanted connection to it.
In the prior art, such a fault is diagnosed by virtue of the two receiver signals (sine and cosine) no longer being present. Such a diagnosis is inadequate, however, because the absence of the sine and cosine signals can also have other causes, e.g. an open excitation line. The fault cannot be narrowed down further on the basis of the mere signals on the signal lines.